Aunt Polly is the aunt and primary guardian of Tom Sawyer, having taken him and his half-brother Sid into her home in the village of St. Petersburg after the death of her sister, who was Tom’s mother. As the head of the Sawyer household, she is a kind-hearted and well-meaning woman who genuinely wants what is best for the boys in her care.

Her personality is defined by a central internal conflict. She feels a deep, abiding love for her nephew Tom, which often prevents her from carrying out the punishments she knows he deserves. As she herself admits, every time she lets him off, her conscience hurts her, but every time she hits him, her old heart nearly breaks. This struggle makes her a figure of the orderly adult world, constantly trying to instill discipline, good manners, and civilized behavior in a boy who is forever seeking adventure and mischief. She is religious and her life is guided by a mixture of scripture and folk wisdom, frequently quoting from the Bible and leading the family in worship. She also has a simple, trusting nature, believing herself to be skilled at clever and mysterious diplomacy, though her attempts to outsmart Tom are almost always unsuccessful.

Aunt Polly's primary motivation is to raise Tom into a good, respectable, and well-behaved young man. She feels a strong sense of responsibility for him, not only as his guardian but also because he is her deceased sister's child, which makes her want to be lenient even when she knows she should be strict. Her efforts to fulfill this role, however, are constantly thwarted by Tom's cleverness and her own soft heart. She employs a variety of methods to enforce her rules, including making him perform tedious chores like whitewashing a fence, hitting him on the head with her thimble as a quick punishment, and attempting to set traps to catch him in his lies, such as stitching his shirt collar with a special thread to see if he has been swimming when he was supposed to be in school.

Her most significant relationship is, of course, with Tom. While she is often exasperated by his antics, there is a strong mutual affection between them. Tom genuinely cares for her feelings and is said to feel worse when he makes her cry than if she had physically punished him. This bond creates a dynamic where Tom often outmaneuvers her, but their love for one another remains the foundation of their interactions. Her relationship with Sid, Tom's well-behaved half-brother, is different. She often holds Sid up as a model of proper conduct, a tactic that unintentionally fuels the rivalry between the two boys. She also demonstrates her compassionate nature beyond her family, famously embracing the motherless Huckleberry Finn during a town celebration, showing her kindness extends to all children in need.

In her role within the story, Aunt Polly represents the established, domestic society that Tom constantly tests the boundaries of. Her attempts at discipline and order create the conflicts that lead to many of Tom's famous adventures and schemes. While she does not undergo a dramatic transformation, her character serves as a constant, loving, and frustrated presence whose patience and methods are repeatedly challenged by Tom's growth and his various escapades. Her notable abilities are not physical or intellectual feats, but rather her capacity for unconditional love and forgiveness, as well as her simple faith. She also has a noted interest in patent medicines and quack medical remedies, which she often administers to Tom with unpredictable results. Visually, she is depicted as an older woman who typically wears glasses but prefers to look over the rims rather than through them.